Alloys and electrical resistance



United States Patent Ofiice Re. 24,242 Reissued Dec. 4, 1956 ELECTRICALRESISTANCE ELEMENTS James M. Lohr, Morristown, N. J., assiguor toDriver- Harris Company, Harrison, N. J., a corporation of New JerseyALLOYS AND No Drawing. Original No. 2,581,420, dated January 8,

1952, Serial No. 117,510, September 23, 1949. Application for reissueJune 29, 1956, Serial No. 595,041 16 Claims, (Cl. 75-171) Matterenclosed in heavy brackets appears in the original patent but forms nopart of this reissue specification; matter printed in italics indicatesthe additions made by reissue.

- This invention relates to alloys and more particularly to alloys forelectric resistance units.

In the manufacture of electrical resistance units, an alloy having theproperty of resisting oxidation at high temperature is essential. Thealloys forming the subject rnatter of this invention are characterizedby ability to resist oxidation and by a prolonged life, exceeding thatof other known alloys when used under high temperature conditions. Sincethe introduction of nickel-chromiumiron alloys as electric resistanceunits many developments 7 have occurred that have improved theirresistance to oxidation. In a number of prior patents I have disclosedand claimed various alloying additions of calcium, zir- 'coniumandaluminum which greatly improve the life of heating elements. It has alsobeen proposed to add rare earth metals, such as cerium, tonickel-.chromium-iron alloys to improve the. life of the heatingelements.

' '.I have found that such combinationof addition elements greatlyincreases the period of life of nickel-chromium- ,iron alloys whenemployed under conditions where they 'aresubjected to high temperatures.The alloy's forming the subject matter of the, present invention mayalso contain small amounts of either silicon or manganese or both P ofthese elements. The rare earth metals may be added as Misch Metal havingan approximate composition of 45 percent cerium, 30 percent lanthanum,20 percent ytterbium and didymium. Although it is convenient to add therare earth metals in the form of Misch Metal, I do not restrict myselfto the use of this material as one or more of the rare earth metals maybe added singly and its effect is of a similar nature. The additions maybe used to advantage with the nickel-chromium-iron alloys of which thebest known examples are the alloys of 30 to 70 percent nickel, 10 to 25percent chromium, balance iron. However, the proportions of these alloysmay be varied with the nickel forming a substantial part of the alloys.The claims of this application are directed to an alloy containing 50 to70 percent nickel. Alloys containing from 30 to 50 percent nickel formthe subject matter of a divisional application, Serial No. 252,198,filed October 19, 1951, now Patent No. 2,687,954.

In the examples hereinafter described, the additions were made to thealloys consisting of substantially 60 percent nickel, percent chromiumand balance iron. Rare earth metals, such as Misch Metal, with calciumand aluminum may be added to such alloys with or without silicon. Theproportions of nickel in such alloys may vary from 50 to 70 percent andthe chromium from 10 to 20 percent with the balance iron, Employingnickelchromium-iron alloys of these proportions, I have added calcium,aluminum and Misch Metal in the quantities or amounts hereinaftermentioned.

In preparingv alloys containing the addition elements above mentioned,the quantities of such addition elements are subtracted from the ironcontent. For example, when additions are made to base alloys containing50 to 70 percent nickel, 10 to 25 percent chromium, the final alloyswill contain 50 to 70 percent nickel, 10 to 25 percent chromium, theaddition elements calcium, aluminum and the rare earth metals in thepercentages hereinafter stated, and the balance iron. While thepropositions 'of calcium, aluminum and rare earth metals may vary Withincertain limits, I have found that the best results are obtained whenthese materials are present in'the final alloys within the followinglimits:

' Percent Calcium .01-.20 Aluminum .011.0 Rare earth metals 'Trace0.50

If the alloys contain manganese,-silicon, or carbon, they may be present.within the following limits:

, Percent Manganese .0 2-4.0 Silicon .20-3.0 Carbon 0.25 max.

While alloys having the properties desired to a very high degreeare'obtained within the limits before mentioned, the preferred range ofaddition elements is as follows:

-Alloys so prepared have been tested for resistance to oxidation at hightemperature by the method approved by the American Society for Testing.Materials Accelerated Life Test for Metallic Materials, B7639.Inconducting such test, the alloy is produced in the form of a wire,drawn 'to a diameter of approximately .025 and tested at a temperatureof 2050 F. The useful life" in hoursv for wire of prior compositions incurrent production containing .04 percent calcium, .10 percent zirconiumand .12 percent aluminum is of the order of 200 hours. The useful lifeof alloys of the present invention, according to the above describedtest, is of the order of 500 to 700 hours. Thus, the useful life isincreased 250 to 300 percent over that of the alloys containing thecalcium, zirconium, aluminum group when the rare earth metals are addedwith calcium and aluminum in the proportions herein stated.

The alloys are prepared in the usual manner by placing the ingredientsin a bath, heating until the alloying elements become molten and thenpouring. In adding rare earth metals to a molten bath, it is necessaryto add considerably larger quantities than will be found in the castmetal because they vaporize readily and pass out of the bath. In manyinstances, with additions of the rare earth metals only a spectrographictrace of one or more of the rare earth metals is found in the castmaterial. The presence of such traces, however, in combination withcalcium and aluminum, greatly increases the oxidation resistanceincrease of percent in resistance is known as the useful life. The lifeof the testerl specimen to burn-out is known Q "35-15 alloys in whichthe alloys contain 30 to 40% nickel,

10 to 25% chromium, and balance iron. The addition elements are presentin substantially thesame proportions as heretofore stated in connectionwith the 60-15 alloys, which contain substantially 60% nickel,substantially 10 to chromium, balance iron.

I claim: I

1. A nickel-chromium-iron alloy consisting essentially of 50 to 70percent nickel, 10 to percent chromium, .01 to .20 percent calcium, .01to 1.0 percent aluminum, a trace to .50 percent of a rare earth metal,balance essentially iron.

2. A nickel-chromium-iron alloy consisting essentially of 50 to 70percent nickel, 10 to 25 percent chromium, substantially .04 percentcalcium, .07 to .40 percent aluminum, a trace to .20 percent of a rareearth metal, balance essentially iron.

3. A nickel-chromium-iron 'alloy consisting essentially of substantially60 percent nickel, substantially 15- percent chromium, .01 to .20percent calcium, .01 to 1.0 percent aluminum, a trace to .50 percent ofa rare earth metal, balance essentially iron.

4. A nickel-chromium-iron alloy consisting essentially of substantially60 percent nickel, substantially 15 percent chromium, substantially .04percent calcium, .07 to .40 percent aluminum, a trace to .20 percent ofa rare earth metal, balance essentially iron.

5. A nickel-chromium-iron alloy consisting essentially of 50 to 70percent nickel, 10 to 25 percent chromium, .01 to .20 percent calcium,.01 to 1.0 percent aluminum, a trace to .50 percent of cerium andlanthanum, balance essentially iron.

6. A nickel-chromium-iron alloy consisting essentially of substantially60 percent nickel, substantially 15' percent chromium, .01 to .20percent calcium, .01 to 1.0 percent aluminum, a trace to .50 percent ofcerium and lanof substantially 60 percent nickel, substantially 15percent chromium, substantially .04 percent ca1cium,.07 to .40 percentaluminum, a trace to .20 percent ofcerium and lanthanum, balanceessentially iron.

9. An electric resistance element consisting essentially of to 70percent nickel, 10 to 25 percent chromium, .01 to .20 percent calcium,.01 to 1.0 percent aluminum, a trace to .5 0 percent of a rare earthmetal, balance essentially iron.

10. An electric resistance element consisting essentially of 50 to 70percent nickel,10 to 25 percent chromium, substantially .04 percentcalcium, .07 to .40 percent aluminum, a trace to .20 percent of a rareearth metal, balance essentially iron.

11. An electric resistance element consisting essentially ofsubstantially percent nickel, substantially 15 percent chromium, .01-to.20 percent calcium, .0] to 1.0 percent aluminum, a trace to .50 percentof a rare earth metal, balance essentially iron.

12. An electric resistance element consisting essentially ofsubstantially 60 percent nickel, substantially 15 percent chromium,substantially .04 percent calcium, .07 to .40 percent aluminum, a traceto .20 percent of a rare earth metal, balance essentially iron.

13. An electric resistance element consisting essentially of 50 topercent nickel, 10 to 25 percent chromium, .01 to .20 percent calcium,.0] to 1.0 percent aluminum, a trace to .50 percent of cerium andlanthanum, balance essentially iron.

14. An electric resistance element consisting essentially ofsubstantially 60 percent nickel, substantially 15 percent chromium, .01to .20 percent calcium, .01 to 1.0 percent aluminum, a trace to .50percent of cerium and lanthanum, balance essentially iron.

15. An electric resistance element consisting essentially of 50 to 70percent nickel, 10 to 25 percent chromium, substantially .04 percentcalcium, .07 to .40 percent aluminum, a trace to .20 percent of ceriumand lanthanum, balance essentially iron.

16. An electric resistance element consisting essentially ofsubstantially 60 percent nickel, substantially 15 percent chromium,substantially .04 percent calcium, .07 to .40

' percent aluminum, a trace to .20 percent of cerium and lanthanum,balance essentially iron.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS 2,005,431 Lohr June 18, 1935 2,047,916 Lohr July14, 1936 2,047,917. Lohr July 14, 1936 2,047,918 Lohr July 14, 1936FOREIGN PATENTS 488,926 Great Britain July 12, 1948

